Robotic surgical systems, instrument drive units, and drive assemblies

ABSTRACT

A drive assembly of an instrument drive unit, is provided. The drive assembly includes a drive screw, a drive nut, a follower, a biasing element, and a drive element. The drive nut is threadedly engaged with a threaded portion of the drive screw such that rotation of the drive screw results in longitudinal movement of the drive nut. The follower is longitudinally slidable with respect to the drive screw. The biasing element is disposed in mechanical cooperation with the drive nut and the follower. The drive element is disposed in mechanical cooperation with the follower. Longitudinal translation of the drive element is configured to drive a function of the surgical instrument.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 16/931,564, filed on Jul. 17, 2020, which is a continuation ofU.S. patent application Ser. No. 16/570,393, filed on Sep. 13, 2019, nowU.S. Pat. No. 10,743,955, which is a continuation of U.S. patentapplication Ser. No. 15/549,005, filed on Aug. 4, 2017, now U.S. Pat.No. 10,420,620, which is a U.S. National Stage Application filed under35 U.S.C. § 371(a) of International Patent Application Serial No.PCT/US2016/021432, filed Mar. 9, 2016, which claims the benefit of andpriority to U.S. Provisional Patent Application Ser. No. 62/130,669,filed Mar. 10, 2015, the entire disclosure of each of which areincorporated by reference herein.

BACKGROUND

Robotic surgical systems have been used in minimally invasive medicalprocedures. Some robotic surgical systems include a console supporting arobot arm, and at least one end effector such as forceps or a graspingtool that is mounted to the robot arm via a wrist assembly. During amedical procedure, the end effector and the wrist assembly are insertedinto a small incision (via a cannula) or a natural orifice of a patientto position the end effector at a work site within the body of thepatient.

Cables extend from the robot console, through the robot arm, and connectto the wrist assembly and/or end effector. In some instances, the cablesare actuated by means of motors that are controlled by a processingsystem including a user interface for a surgeon or clinician to be ableto control the robotic surgical system including the robot arm, thewrist assembly and/or the end effector.

In some instances, the wrist assembly provides three degrees of freedomfor movement of the end effector through the use of cables or cablepairs, one for each degree of freedom. For example, for grasping orcutting end effectors, the wrist assembly provides the three degrees offreedom by allowing changes to a pitch, a yaw, and an opening andclosing of the end effector.

Prior to or during use of the robotic system, surgical instruments areselected and connected to instrument drive units of each robot arm. Forproper installation to be completed, certain connecting features of thesurgical instrument must be matingly engaged to corresponding connectingfeatures of the instrument drive unit. Once these features are matinglyengaged, the instrument drive unit can drive the actuation of thesurgical instrument. However, cables for actuating functions of thesurgical instrument can lose their tension force and become slack uponmanipulation of the jaw members of the surgical instrument, for example.

Accordingly, there is a need for instrument drive units that maintaintension in these cables both in a passive state and in an active state.

SUMMARY

The present disclosure relates to a drive assembly of an instrumentdrive unit for use with a surgical instrument. The drive assemblyincludes a drive screw, a drive nut, a follower, a biasing element, anda drive element. The drive screw defines a longitudinal axis andincludes a threaded portion. The drive nut is threadedly engaged withthe threaded portion of the drive screw such that rotation of the drivescrew results in longitudinal movement of the drive nut. The follower islongitudinally slidable with respect to the drive screw. The biasingelement is disposed in mechanical cooperation with the drive nut and thefollower. The drive element is disposed in mechanical cooperation withthe follower. Longitudinal translation of the drive element isconfigured to drive a function of the surgical instrument.

In disclosed embodiments, the follower is disposed proximally of thedrive nut, and the follower is biased proximally.

It is also disclosed that the drive element is secured to the follower,and that the drive element is longitudinally translatable with respectto the drive nut.

It is further disclosed that each of the drive nut and the followerincludes a retention pocket configured to house a portion of the biasingelement.

In disclosed embodiments, the biasing element is a compression spring.

Additionally, it is disclosed that the follower is disposed proximallyof the drive nut, and the drive element extends distally from thefollower.

It is also disclosed that the follower is non-threadedly engaged withthe drive screw.

It is further disclosed that the drive member includes a flexible cable.

In disclosed embodiments, the drive nut defines an aperture, thefollower defines an aperture, and the drive screw extends through theaperture of the drive nut and through the aperture of the follower. Itis also disclosed that the biasing element is disposed about the drivescrew.

The present disclosure also relates to an instrument drive unit for usewith a surgical instrument. The instrument drive unit includes aplurality of drive assemblies. Each drive assembly includes a drivescrew, a drive nut, a biasing element, and a flexible drive element. Thedrive screw defines a longitudinal axis, and includes a threadedportion. The drive nut is threadedly engaged with the threaded portionof the drive screw such that rotation of the drive screw results inlongitudinal movement of the drive nut. The biasing element is disposedin mechanical cooperation with the drive nut. The flexible drive elementis disposed in mechanical cooperation with the biasing element.Longitudinal translation of the flexible drive element is configured todrive a function of jaw members of the surgical instrument.

In disclosed embodiments, each drive assembly further includes afollower longitudinally slidable with respect to the drive screw.

It is further disclosed that the biasing element is configured tomaintain the flexible drive element in a tensile state duringapplication of a mechanical force to the jaw members of the surgicalinstrument.

Additionally, it is disclosed that the biasing element is a compressionspring.

It is also disclosed that the drive nut defines an aperture, and thatthe drive screw extends through the aperture of the drive nut. It isfurther disclosed that the biasing element is disposed about the drivescrew.

In disclosed embodiments, the plurality of drive assemblies includesfour drive assemblies.

It is further disclosed that the instrument drive unit includes ahousing, and that each drive assembly of the plurality of driveassemblies is housed at least partially within the housing. The flexibledrive element of each drive assembly extends through a central bore ofthe housing.

In disclosed embodiments, the drive nut and/or the follower include arail that is configured to slidingly engage a channel of the housing.

Further details and aspects of exemplary embodiments of the presentdisclosure are described in more detail below with reference to theappended figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure are described herein withreference to the accompanying drawings, wherein:

FIG. 1A is a schematic illustration of a medical work station andoperating console in accordance with the present disclosure;

FIG. 1B is a schematic, perspective view of a motor of a control deviceof the medical work station of FIG. 1A;

FIG. 1C is a perspective view of an instrument drive unit in accordancewith embodiments of the present disclosure;

FIG. 2 is enlarged view of the area of detail indicated in FIG. 1C;

FIG. 3 is a distally-facing perspective view of a portion of theinstrument drive unit of FIGS. 1C and 2 with various parts removedtherefrom;

FIG. 4 is an exploded view of the instrument drive unit of FIGS. 1C-3 ;

FIGS. 5-7 are perspective views of a drive assembly of the instrumentdrive unit of FIGS. 1C-4 shown at various points of operation;

FIG. 8 is an exploded view of the drive assembly of FIGS. 5-7 ;

FIG. 9 is a perspective, cross-sectional view of the drive assembly ofFIGS. 5-8 , as taken along line 9-9 of FIG. 5 ;

FIG. 10 is a cross-sectional view of the instrument drive unit of thepresent disclosure taken along line 10-10 of FIG. 2 ;

FIG. 11 is a cross-sectional view of the instrument drive unit of thepresent disclosure taken along line 11-11 of FIG. 2 ;

FIG. 12 is a transverse cross-sectional view of the instrument driveunit of the present disclosure taken along line 12-12 of FIG. 11 ; and

FIG. 13 is a transverse cross-sectional view of the instrument driveunit of the present disclosure taken along line 13-13 of FIG. 11 .

DETAILED DESCRIPTION

Embodiments of the presently disclosed instrument drive units aredescribed in detail with reference to the drawings, in which likereference numerals designate identical or corresponding elements in eachof the several views. As used herein the term “distal” refers to thatportion of the instrument drive unit that is farther from the user,while the term “proximal” refers to that portion of the instrument driveunit that is closer to the user.

Referring initially to FIGS. 1A and 1B, a medical work station is showngenerally as work station 1 and generally includes a plurality of robotarms 2, 3; a control device 4; and an operating console 5 coupled withcontrol device 4. Operating console 5 includes a display device 6, whichis set up in particular to display three-dimensional images; and manualinput devices 7, 8, by means of which a person (not shown), for examplea surgeon, is able to telemanipulate robot arms 2, 3 in a firstoperating mode, as known in principle to a person skilled in the art.

Each of the robot arms 2, 3 includes a plurality of members, which areconnected through joints, and an instrument control unit 100, to whichmay be attached, for example, a surgical instrument 10 having aninstrument drive unit 200, and supporting an end effector 20 having jawmembers 22 and 24, in accordance with the embodiments of instrumentdrive units 200 disclosed herein, as will be described in greater detailbelow.

Robot arms 2, 3 may be driven by electric drives (not shown) that areconnected to control device 4. Control device 4 (e.g., a computer) isset up to activate the drives, in particular by means of a computerprogram, in such a way that robot arms 2, 3, instrument control units100, and thus the surgical instruments 10 execute a desired movementaccording to a movement defined by means of manual input devices 7, 8.Control device 4 may also be set up in such a way that it regulates themovement of robot arms 2, 3 and/or of the drives.

Medical work station 1 is configured for use on a patient 13 lying on apatient table 12 to be treated in a minimally invasive manner by meansof surgical instrument 10. Medical work station 1 may also include morethan two robot arms 2, 3, the additional robot arms likewise beingconnected to control device 4 and being telemanipulatable by means ofoperating console 5. An instrument control unit and a surgicalinstrument may also be attached to the additional robot arm. Medicalwork station 1 may include a database 14, in particular coupled to withcontrol device 4, in which are stored for example pre-operative datafrom patient 13 and/or anatomical atlases.

Reference may be made to U.S. Patent Publication No. 2012/0116416, filedon Nov. 3, 2011, now U.S. Pat. No. 8,828,023, entitled “MedicalWorkstation,” the entire content of which is incorporated herein byreference, for a detailed discussion of the construction and operationof medical work station 1.

Control device 4 may control a plurality of motors (e.g., “M1”-“M6”).Motors may be part of instrument control unit 100 and/or disposedexternally of instrument control unit 100. Motors “M” (e.g., motors “M”being located externally of instrument control unit 100) may beconfigured to rotate a crown gear “CG” (FIG. 1B), or the like, that iskeyed to or non-rotatably supported on a rotatable shaft of at leastsome of motors “M.” In use, as motors “M” are driven, the rotation ofcrown gear(s) “CG” effects operation and/or movement of instrument driveunit 200 of surgical instrument 10, as discussed below. It is furtherenvisioned that at least one motor “M” receives signals wirelessly(e.g., from control device 4). It is contemplated that control device 4coordinates the activation of the various motors (Motor 1 . . . n) tocoordinate an operation and/or movement of surgical instrument 10. It isenvisioned that each motor corresponds to a separate degree of freedomof surgical instrument 10 engaged with instrument control unit 100. Itis further envisioned that more than one motor, including every motor(Motor 1 . . . n), is used for each degree of freedom. Reference may bemade to commonly owned International Patent Application No.PCT/US14/61329, filed on Oct. 20, 2014 entitled “Wrist and JawAssemblies for Robotic Surgical Systems,” the entire content of which isincorporated herein by reference, for a detailed discussion ofillustrative examples of the construction and operation of end effectors20 for use with instrument control unit 100.

Turning now to FIGS. 1C-13 , instrument drive unit 200 is shown havingsurgical instrument 10 extending distally therefrom, and which isconfigured to engage instrument control unit 100, as described above.Instrument drive unit 200 is configured to transfer rotational movementsupplied by instrument control unit 100 (e.g., via motors “M”) intolongitudinal movement of drive members 380 to effect various functionsof end effector 20.

With reference to FIGS. 2-4 , instrument drive unit 200 includes ahousing assembly 205 which includes a proximal housing 210 and a distalhousing 220. Proximal housing 210 and distal housing 220 are releasablycoupled to each other, which may facilitate assembly of instrument driveunit 200, and which may facilitate access, repair, and/or replacement ofparts housed at least partially therein. Housing assembly 205 defines atleast one bore 207 for housing drive assemblies 300. It is envisionedthat housing assembly 205 includes four separate bores 207, where eachbore 207 is at least partially separated from each other and where eachbore 207 is configured to house a single drive assembly 300.Additionally, as discussed below, bore 207 includeslongitudinally-extending channels 206 (e.g., four channels 206) therein.Each channel 206 is configured to slidingly accept a rail 353 of drivenut 350 and a rail 363 of follower 360. It is further envisioned thateach bore 207 includes two separate channels 206, where one channel 206is configured to slidingly accept rail 353 of drive nut 350 and wherethe other channel 206 is configured to slidingly accept rail 363 offollower 360

With continued reference to FIGS. 2-4 , instrument drive unit alsoincludes a plurality of drive assemblies 300. In the illustratedembodiment, instrument drive unit 200 includes four drive assemblies300, however instrument drive unit 200 may include more (e.g., five orsix) or fewer (e.g., three) drive assemblies 300 without departing fromthe scope of the present disclosure.

With reference to FIGS. 5-9 , each drive assembly 300 includes aproximal gear 310, a proximal bearing 320, a distal bearing 330, a drivescrew 340, a drive nut 350, a follower 360, a biasing element 370, anddrive member (e.g., a flexible cable) 380. Proximal gear 310 isconfigured to engage with an instrument control gear (e.g., crown gear“CG” of motor “M”) of instrument control unit 100, such that rotation ofcrown gear “CG” causes a corresponding rotation of proximal gear 310.Proximal gear 310 may be a crown gear “CG” that is configured to matewith and/or mesh with crown gear “CG” of motor “M.”

With particular reference to FIGS. 8 and 9 , proximal gear 310 includesan aperture 312 extending longitudinally therethrough, which isconfigured to mechanically engage a proximal portion 342 of drive screw340. As shown, aperture 312 and proximal portion 342 of drive screw 340have corresponding, non-circular cross-sections, such that proximal gear310 and drive screw 340 are keyed to one another, which results in arotationally fixed connection therebetween. Accordingly, rotation ofproximal gear 310 results in a corresponding rotation of drive screw340.

Proximal bearing 320 is disposed about a proximal shaft 343 of drivescrew 340 adjacent a portion of proximal housing 210, and distal bearing330 is disposed about a distal shaft 344 of drive screw 340 adjacent aportion of distal housing 220 (see FIG. 10 , for example). Each ofproximal bearing 320 and distal bearing 330 permits or facilitatesrotation of drive screw 340 with respect to housing assembly 205.Additionally, proximal bearing 320 may be configured to function as aproximal stop for follower 360, and distal bearing 330 may be configuredto function as a distal stop for drive nut 350.

Drive screw 340 includes proximal portion 342, proximal shaft 343,distal shaft 344 and a threaded portion 345, and defines a longitudinalaxis “A-A” extending through a radial center thereof (see FIG. 8 ).Rotation of proximal gear 310 causes drive screw 340 to rotate aboutlongitudinal axis “A-A” in a corresponding direction and rate ofrotation.

Drive nut 350 includes a threaded aperture 352 extending longitudinallytherethrough, which is configured to mechanically engage threadedportion 345 of drive screw 340. Drive nut 350 is configured to bepositioned on drive screw 340 in a manner such that rotation of drivescrew 340 causes longitudinal movement of drive nut 350. That is, drivenut 350 and drive screw 340 are threadedly engaged with each other.Moreover, rotation of proximal gear 310 in a first direction (e.g.,clockwise) causes drive nut 350 to move in a first longitudinaldirection (e.g., proximally) with respect to proximal portion 342 ofdrive screw 340, and rotation of proximal gear in a second direction(e.g., counter-clockwise) causes drive nut 350 to move in a secondlongitudinal direction (e.g., distally) with respect to proximal portion342 of drive screw 340. Drive nut 350 also includes a retention pocket354 disposed proximally adjacent threaded aperture 352. Retention pocket354 includes a larger inner diameter than threaded aperture 352, and isconfigured to house at least a portion of biasing element 370, asdiscussed in further detail below.

Drive nut 350 includes rail 353 extending longitudinally along an outersurface thereof, and which is configured to be slidably disposed in alongitudinally extending channel 206 formed in bore 207 of housingassembly 205 (see FIGS. 5-7 and 12 , for example). Rail 353 of drive nut350 cooperates with channel 206 of bore 207 of housing assembly 205 toinhibit or prevent drive nut 350 from rotating about longitudinal axis“A-A” as drive screw 340 is rotated.

Follower 360 includes rail 363 extending longitudinally along an outersurface thereof, and which is configured to be slidably disposed inlongitudinal extending channel 206 formed in bore 207 of housingassembly 205 (see FIGS. 3, 5-7 and 12 , for example). Rail 363 offollower 360 cooperates with channel 206 of bore 207 of housing assembly205 to inhibit or prevent follower 360 from rotating about longitudinalaxis “A-A” as drive screw 340 is rotated.

Follower 360 includes a non-threaded aperture 362 extendinglongitudinally therethrough, which is configured to slidingly engagethreaded portion 345 of drive screw 340. That is, follower 360 isnon-threadedly engaged with and slidably supported on drive screw 340.It is also disclosed that follower 360 does not engage drive screw 340,and that follower 360 is solely guided by the geometry (e.g., e.g.,channel 206) of housing assembly 205. Follower 360 includes a retentionpocket 364 disposed distally adjacent aperture 362. Retention pocket 364includes a larger inner diameter than aperture 362, and is configured tohouse at least a portion of biasing element 370, as discussed in furtherdetail below. Follower 360 also includes an engagement portion 366disposed adjacent a radially outward surface thereof, which isconfigured to mechanically engage a proximal portion 382 of drive member380.

In the illustrated embodiment, follower 360 is disposed proximally ofdrive nut 350, but the present disclosure also includes embodimentswhere follower 360 is disposed distally of drive nut 350. In suchembodiments, retention pocket 354 of drive nut 350 would be disposed ata distal location thereof, and retention pocket 364 of follower 360would be disposed at a proximal location thereof. Here, it is envisionedthat follower 360 pushes drive member 380 distally, rather than follower360 pulling drive member 380 proximally.

Biasing element 370, e.g., a compression spring, is configured toradially surround a portion of threaded portion 345 of drive screw 340.That is, drive screw 340 extends through an aperture 371 defined by andextending longitudinally through biasing element 370. Additionally, asseen in FIG. 9 , a proximal portion 372 of biasing element 370 isconfigured for reception at least partially within retention pocket 364of follower 360, and a distal portion 374 of biasing element 370 isconfigured for reception at least partially within retention pocket 354of drive nut 350. In disclosed embodiments, proximal portion 372 ofbiasing element 370 is immovably fixed to follower 360, and distalportion 374 of biasing element 370 is immovably fixed to drive nut 350.It is envisioned that a compressed length of biasing element 370 isequal to or slightly smaller than a combined longitudinal length ofretention pocket 364 of follower 360 and retention pocket 354 of drivenut 350, thus allowing contact between a proximal face 351 of drive nut350 and a distal face 361 of follower 360 (see FIG. 6 ). While theillustrated embodiments show a particular type of biasing element 370(i.e., a compression spring), other types of biasing elements arecontemplated by the present disclosure.

Drive member 380 extends distally from follower 360, through a centralbore 208 (FIGS. 2 and 10 ) of housing assembly 205, and is configured tomechanically engage a portion of surgical instrument 10, e.g., endeffector 20. More particularly, each drive assembly 300 is orientedwithin housing assembly 205 such that the drive member 380 of each driveassembly 300 is centrally located within housing assembly 205 (see FIGS.10-13 ), and extends through an elongated portion of surgical instrument10 and into engagement with end effector 20, for example. It isenvisioned that the surgical instrument 10 includes projections or thelike to help guide or route drive members 380 between the drive assembly300 and the end effector, for example.

Longitudinal translation of drive member 380 is configured to drive afunction of end effector 20. For example, distal translation of aparticular drive member 380 may be configured to approximate jaw members22 and/or 24 with respect to the other, and proximal translation ofdrive member 380 may be configured to move at least one jaw member 22away from the other jaw member 24, for instance. Additionally, distaltranslation of a drive member 380 of a different drive assembly 300 ofinstrument drive unit 200 may be configured to articulate jaw members22, 24 in a first direction, and proximal translation of the this drivemember 380 may be configured to articulate jaw members 22, 24 in asecond direction.

Additionally, since drive member 380 may be flexible and follow aparticular path through surgical instrument 10, including a centralportion of housing assembly 205, it may be beneficial to maintain drivemember 380 in tension to prevent slack or to reduce the amount of slackin drive member 380. Without the benefit of the present disclosure, auser who manually (e.g., by hand) opens or otherwise manipulates jawmembers to inspect and/or clean the jaw members, for example, may exerta proximal force on at least one drive member. That is, opening jawmembers of a surgical instrument may cause at least a portion of atleast one of its drive members to move proximally. In systems wheredrive members are directly connected to a drive nut, and where the drivenut is threadedly engaged with a drive screw, the engagement between thedrive screw and the drive nut would prevent proximal translation of thedrive nut in response to proximal translation of the drive member.Accordingly, proximal movement of the drive member (e.g., caused bymanipulating the jaw members) may cause the drive member to go slack,and may cause the drive member to fall off of pulleys within thesurgical instrument and/or become dislodged from retention pockets, forexample. Instrument drive unit 200 of the present disclosure prevents orminimizes the possibility of drive members 380 losing their tension andgoing slack.

During a use of instrument drive unit 200 in the active state (i.e.,when motor(s) “M” of instrument control unit 100 are used to rotateproximal gear(s) 310), rotation of proximal gear 310 results in acorresponding rotation of drive screw 340. Rotation of drive screw 340causes longitudinal translation of drive nut 350 due to the engagementbetween threaded portion 345 of drive screw 340 and threaded aperture352 of drive nut 350. As discussed above, the direction of longitudinaltranslation of drive nut 350 is determined by the direction of rotationof proximal gear 310, and thus drive screw 340. With particularreference to FIG. 6 , which illustrates proximal face 351 of drive nut350 abutted against distal face 361 of follower 360 (i.e., in the activestate), proximal translation of drive screw 340 results in acorresponding proximal translation of follower 360, and thus acorresponding proximal translation of a respective drive member 380which is engaged with follower 360.

Additionally, when one drive nut 350 moves in a first longitudinaldirection (e.g., proximally), it is envisioned that a drive nut 350 froma different drive assembly 300 is forced to correspondingly move in asecond, opposite longitudinal direction (e.g., distally). Suchconfigurations function to compensate for any slack in drive members380. Moreover, once all drive nuts 350 are engaged with respectivefollowers 360 (e.g., compressing biasing element 370; see FIG. 6 ), andwhen the system is so-called “stiff” (i.e., no stretch in drive members380), the sum of the displacements of the four drive members 380 must bezero. For example, if one drive member 380 moves distally two units, twoother drive members 380 can move proximally one unit each, and thefourth drive member 380 would not move, thus preserving the net zerodisplacement.

This movement of drive nuts 350, followers 360 and drive members 380 iscontrolled by motors “M” and system controls. When a drive nut 350 movesdistally without corresponding proximal movement of a drive member 380,the drive nut 350 would separate from follower 360 with that driveassembly 300 (see FIGS. 5 and 7 ). These features help achieve zerodisplacement by preventing slack in drive members 380.

More particularly, in FIGS. 5 and 7 , drive nut 350 has separated fromfollower 360. Here, this drive assembly 300 may not be capable ofeffectively translating a meaningful load to drive member 380, but drivemember 380 and follower 360 are capable of translating relatively freely(or unimpeded) proximally and distally. Such a configuration or abilityis helpful to allow a wrist assembly to be externally manipulatedseparate from the system control. In FIG. 5 , drive nut 350 has beendriven proximally such that biasing element 370 has been partiallycompressed; in FIG. 7 biasing element 370 has been compressed less thanin FIG. 5 (e.g., biasing element 370 has not been compressed).

In FIG. 6 , drive assembly 300 is in an “active use state” where drivenut 350 has been driven into contact with follower 360, and pre-tensionhas been added to drive member 380, for example. When each of the fourdrive assemblies 300 is in this position, the system is notbackdrivable; an external force on the jaw members 22, 24 or wristassembly would not result in movement of drive assemblies 300.

During use of instrument drive unit 200 in the passive state (i.e., whenjaw members 22, 24 are being manipulated manually), manual manipulationof jaw members 22, 24 results in longitudinal movement of follower 360while maintaining some level of tension of drive member 380. Moreparticularly, in disclosed embodiments, manipulation of jaw members 22,24 (e.g., moving one jaw member 22 away from the other 24) causesproximal movement of one drive member 380. As described above, proximalmovement of a drive member in a different instrument (not employing theprinciples of the present disclosure) may cause the drive member to loseits tension or stretch and thus cause undesirable effects. Here,however, proximal movement of the one drive member 380 results in acorresponding proximal movement of follower 360 because follower 360 isslidable with respect to drive screw 340 and is not threadedly engagedtherewith. At least some level tension in drive member 380 remainsbecause biasing element 370, which is engaged with both follower 360 anddrive nut 350, provides an opposite force against follower 360. That is,if the one drive member 380 is moved proximally, and thus exerts aproximal force on follower 360, this force is resisted and/orcounterbalanced by biasing element 370, thus retaining tension in drivemember 380. Likewise, if the one drive member 380 is moved distally andthus exerts a distal force on follower 360, this force is also resistedand/or counterbalanced by biasing element 370, thus retaining at leastsome level of tension in drive member 380.

The present disclosure includes a robotic surgical system including aninstrument drive unit 200, an instrument control unit 100 including fourindependently-controlled motors “M,” and a surgical instrument 10including four drive assemblies 300, with each drive assembly 300selectively connectable to a respective motor “M” of instrument controlunit 100, for example, as described above. Additionally, the presentdisclosure includes methods of controlling a surgical instrument 10including the use of instrument control unit 100 and instrument driveunit 200, and methods of performing a surgical task using instrumentcontrol unit 100 and instrument drive unit 200. The present disclosurefurther includes methods of manually manipulating jaw members 22, 24while maintaining tension in drive members 380.

It will be understood that various modifications may be made to theembodiments disclosed herein. Therefore, the above description shouldnot be construed as limiting, but merely as exemplifications of variousembodiments. Those skilled in the art will envision other modificationswithin the scope and spirit of the claims appended thereto.

What is claimed is:
 1. A drive assembly for use with a surgicalinstrument, the drive assembly comprising: a drive screw defining alongitudinal axis; a drive unit threadedly engaged with a portion of thedrive screw and being longitudinally movable relative to the drivescrew; a follower disposed in mechanical cooperation with the drivescrew and being longitudinally movable relative to the drive screw andrelative to the drive unit; and a biasing element disposed in mechanicalcooperation with the follower, wherein the follower includes a retentionpocket configured to house a portion of the biasing element.
 2. Thedrive assembly according to claim 1, further including a drive memberdisposed in mechanical cooperation with the follower.
 3. The driveassembly according to claim 2, wherein longitudinal translation of thedrive member relative to the drive screw is configured to drive afunction of the surgical instrument.
 4. The drive assembly according toclaim 2, wherein the drive member extends distally from the follower. 5.The drive assembly according to claim 4, wherein the follower isdisposed proximally of the drive unit.
 6. The drive assembly accordingto claim 1, wherein the biasing element is disposed between the driveunit and the follower.
 7. The drive assembly according to claim 6,wherein the biasing element is coaxial with the drive screw.
 8. Thedrive assembly according to claim 6, further including a drive memberdisposed in mechanical cooperation with the follower, wherein thebiasing element is configured to maintain the drive member in a tensilestate during application of a mechanical force to jaw members of thesurgical instrument.
 9. The drive assembly according to claim 1, whereinthe drive unit defines an aperture, and wherein the drive screw extendsthrough the aperture of the drive unit.
 10. The drive assembly accordingto claim 1, wherein the follower is non-threadedly engaged with thedrive screw.
 11. The drive assembly according to claim 1, wherein thedrive unit is configured to house a portion of the biasing element. 12.A drive assembly for use with a surgical instrument, the drive assemblycomprising: a drive screw defining a longitudinal axis; a drive unitengaged with a portion of the drive screw and being longitudinallymovable relative to the drive screw; a biasing element disposed inmechanical cooperation with the drive unit; and a follower disposed inmechanical cooperation with the biasing element, the follower beinglongitudinally translatable relative to the drive screw and including aretention pocket configured to house a portion of the biasing element.13. The drive assembly according to claim 12, wherein the follower isdisposed proximally of the drive unit.
 14. The drive assembly accordingto claim 12, wherein the drive unit defines an aperture, and wherein thedrive screw extends through the aperture of the drive unit.
 15. Thedrive assembly according to claim 14, wherein the biasing elementradially surrounds a portion of the drive screw.
 16. The drive assemblyaccording to claim 12, wherein the follower is disposed proximally ofthe drive unit, and wherein biasing element biases the followerproximally relative to the drive screw.
 17. The drive assembly accordingto claim 12, wherein the drive unit includes a retention pocketconfigured to house a portion of the biasing element.
 18. A driveassembly for use with a surgical instrument, the drive assemblycomprising: a drive unit; a biasing element disposed in mechanicalcooperation with the drive unit; a drive member disposed in mechanicalcooperation with the biasing element; and a follower disposed inmechanical cooperation with the biasing element, the follower beinglongitudinally translatable relative to the drive unit and including aretention pocket configured to house a portion of the biasing element,wherein the biasing element is configured to maintain the drive memberin a tensile state during application of a mechanical force to jawmembers of the surgical instrument.
 19. The drive assembly according toclaim 18, wherein the drive unit includes a retention pocket configuredto house a portion of the biasing element.
 20. The drive assemblyaccording to claim 18, wherein the drive unit, the biasing element, andthe follower are coaxial with each other.